Asymmetric Site-Enabled O–O Coupling in Co₃O₄ for Oxygen Evolution Reaction

The efficiency of hydrogen production from water electrolysis is mainly restricted by the sluggish oxygen evolution reaction (OER). The mainstream adsorbate evolution mechanism and lattice oxygen-mediated mechanism face a trade-off between performance and stability, while the diatomic oxygen mechanism (DOM) based on the O–O coupling provides a solution to overcome this limitation. However, the intrinsic principles that facilitate the O–O coupling remain unclear, which complicates material design. In this work, we use spinel Co3O4 as a model and identify that the asymmetric sites formed by the octahedral Co with O defects and the original octahedral Co are effective sites for O–O coupling. Based on this, we propose using the degree of asymmetry of the dual site as a descriptor to quantify the reaction free energy of rate-determining step along the DOM pathway, presenting a volcano plot relationship. Experimental validation shows that plasma-prepared Co3O4 enables O–O coupling, requiring only 287 and 420 mV overpotentials to achieve current densities of 10 and 1000 mA cm–2 in 0.5 M H2SO4, respectively. This work demonstrates efficient sites for the OER along the DOM pathway in Co3O4, providing valuable insights for designing high-performance OER catalysts.